When BT headset is activated all audio is sent to the headset (Nokia 5800 XpressMusic, S60v5). Can it be made possible to exclude applications from BT audio, so that audio will remain "connected" to the device speaker? Most of all missing that for the navigation software ...
My older Windows-phone did only sent the telephone-audio to the BT headset, it was even possible to hear navigation audio via the device speaker, while I had a phone call on the headset!
When used as mediaplayer/radio with the wired earplugs it is alreadey possible to switch audio to the device-speaker.